Crack Tip Localization in Adhesively Bonded CFRP-CFRP Joints subjected to Mode II Fatigue Loading

The use of resin-based composite materials in place of metals has gained prominence across various industries. Such composites offer a superior strength-toweight ratio, addressing the increasing demand for lightweight structures to reduce emissions. As such, structural joining of composite materials is of growing importance. Traditional fasteners, however, not only compromise weight savings, but also introduce weak points within the structure. Adhesive bonding emerges as the most promising joining technology, balancing weight efficiency and performance. However, its broader adoption for primary structural joints is hindered by a lack of standardization of quality control and non-destructive inspection techniques and concerns about long-term reliability. To address this challenge, the “CERTBOND” COST Action (CA18120) initiative was established to investigate adhesive bonding and develop a reliable certification roadmap for bonded primary structures. As part of this initiative, a Mode II fatigue loading Round Robin study was conducted on adhesively bonded CFRPCFRP End-Notched Flexure specimens. While conducting the fatigue tests, supplementary techniques for estimating the crack tip position were employed. The selected techniques included visual testing (employing two different methods), ultrasonic phased array testing, and distributed strain sensing using optical backscatter reflectometry. The present study describes, compares and discusses the results obtained by the cited localization techniques.